The Plague of Undeath in particular is a magical affliction first summoned by Ner'zhul, the Lich King (under the direction of the demon lord Kil'jaeden), from his icy prison within the Frozen Throne in the land Northrend in order to create the undead army known as the Scourge, which was created to be the harbinger of the Burning Legion.

This article or section includes speculation, observations or opinions possibly supported by lore or by Blizzard officials.*

Significant evidence exists that the plague of undeath in particular is fel in nature. Fel energy, which Chris Metzen once defined as an entropic death energy,[3] is essentially an entropic death energy that can bring things to an entropic state or oblivion. Despite that fact and the. Still, the World of Warcraft: Chronicle Volume 3 refers to the plague that the warlocks used against the draenei as "fel" and plague is plague no matter if it is necromantic or not. Eventually, Ner'zhul spread the contagion to ice trolls, humans, and other creatures. These creatures would be brought to oblivion then rise again as undead. The entity eventually taught Kel'Thuzad the secrets of the necrolyte and commanded the necromancer to formed a cult comprised with acolytes that will worship it as god - a cult that would be known as the Cult of the Damned - and infect grain known as seeds with the demon Mal'ganis watching him. Those that ingested the seeds limn a sickly green, died, then rose as undead. Kel'Thuzad would name the growing army the Scourge.
When Arthas and Jaina found the land around the granary, Jaina was reminded about the land surrounding the Dark Portal and what happened to it. When the demonic fel portal was opened, the demonic fel energies from Draenor spilled into Azeroth and killed the land. Arthas then questioned if perhaps the grain itself could be plagued, carrying demonic fel energy. Jaina said perhaps and continued hunting down Kel'Thuzad. Eventually, they would go hunting for Mal'gnais and discover that those inhabiting Stratholme were infected by plague. While Jaina and Uther were adverse to killing, Arthas was not. Arthas, along with mage-priests and other beings, culled and purged Stratholme.[4]
Eventually, the wily warlock Heigan the Unclean helped the Scourge transform the land into the Plaguelands. There, the Scourge set up a base where they can operate and created plague cauldrons that would spread plague gases into the chaotic element known as air. Creatures and plants grow abormally and this might be a symptom of fel magics. Creation tends to grow thicker when exposed to fel magics. One of the few creatures that thrives in the Plaguelands is the carrion grub. They can reach huge sizes and are immune to the Plague. A prime example of a carrion grub is Borelgore. The Plaguelands also have heavy populations of massive mushrooms which also seem to thrive in these conditions. Fungus in particular may be a conduit for fel plague to be spread.

The Argent Dawn, a regime dedicated to the eradication of the Scourge menace, have discovered ways of sabotaging these cauldrons and reversing their effects, thereby purifying the chemicals within and making them toxic to the undead.

The Plague, while established many times as a very powerful affliction, was proven to be curable at least once.[citation needed] During the end of the Zombie InfestationWorld Event, the Alliance and Horde managed to find cures to the Plague, even if the converted zombies themselves could not be saved.[citation needed] The Plague cannot be healed or weakened by individual means (with exception of the Holy Light regarding weakening the affliction).[citation needed]